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rawgreaze
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Joined: 23 May 2009
Posts: 108
Location: United Kingdom
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 Posted: Fri May 22, 2015 4:45 pm Post subject: [Code Injection] How do I change the float stack value? |
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Say, this is my assembly code.
| Code: |
[ENABLE]
//code from here to '[DISABLE]' will be used to enable the cheat
alloc(newmem,2048)
label(returnhere)
label(originalcode)
label(exit)
newmem: //this is allocated memory, you have read,write,execute access
//place your code here
cmp [ebx+10],1
jne originalcode
fadd dword ptr [ebx+04]
fstp dword ptr [ebp-30]
jmp exit
originalcode:
fsubr dword ptr [ebx+04]
fstp dword ptr [ebp-30]
exit:
jmp returnhere
"Tutorial-i386.exe"+27D7D:
jmp newmem
nop
returnhere:
[DISABLE]
//code from here till the end of the code will be used to disable the cheat
dealloc(newmem)
"Tutorial-i386.exe"+27D7D:
fsubr dword ptr [ebx+04]
fstp dword ptr [ebp-30]
//Alt: db D8 6B 04 D9 5D D0
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Is there a way to change fstp and not use fadd, but physically changing the value of the stack value to make it permanently, say, 1000hp instead of adding every time or so?
EDIT: I tried commenting out both the fsubr and fstp, and put | Code: | | mov [ebp-30],(float)1337 |
instead, but I get "Invalid floating point operation" or some shit.
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Geri
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| Posted: Fri May 22, 2015 4:54 pm Post subject: |
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Just use
mov [ebp-30],(float)1337
right after the fstp instruction and the value will be overwritten with 1337, whatever it was before. There is no need to comment out the fstp.
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rawgreaze
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Joined: 23 May 2009
Posts: 108
Location: United Kingdom
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| Posted: Fri May 22, 2015 4:59 pm Post subject: |
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| Geri wrote: | Just use
mov [ebp-30],(float)1337
right after the fstp instruction and the value will be overwritten with 1337, whatever it was before. There is no need to comment out the fstp. |
Huh. I never thought to leave the fstp instruction in.
How come it creates an error when it's left out, but when it's in it has no erros? Weird.
EDIT: Also, when do you use the square brackets, like in [ebp-30]?
I've seen mov instructions like: mov esp,[myvariable] or something, why?
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Geri
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| Posted: Fri May 22, 2015 5:07 pm Post subject: |
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Read up on what fstp does exactly and you will see. (HINT: You screw up the registers.)
If you really need to get rid of an fstp instruction, you should replace it with
fstp st(0)
Don't nop it, don't comment it.
| Quote: | EDIT: Also, when do you use the square brackets, like in [ebp-30]?
I've seen mov instructions like: mov esp,[myvariable] or something, why? |
The bracket means that you are working with the value on the address inside the bracket.
Eg eax = 44556600
mov ebx,eax //copy 44556600 to ebx
mov ebx,[eax] //copy the value on address 44556600 to ebx
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rawgreaze
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Joined: 23 May 2009
Posts: 108
Location: United Kingdom
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| Posted: Fri May 22, 2015 5:10 pm Post subject: |
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| Geri wrote: | Read up on what fstp does exactly and you will see. (HINT: You screw up the registers.)
If you really need to get rid of an fstp instruction, you should replace it with
fstp st(0)
Don't nop it, don't comment it. |
I read that fstp pushes the float pointer on top of the stack or some shit.
& do all assembly scripts work on restart, or do some need an AoB scan? Like the CETutorial works evry tym, but in other games, does the address of the disassembly thing change?
EDIT: Ohh, shit!
Thanks for explaining the square bracket thing to me ;D
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Geri
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| Posted: Fri May 22, 2015 5:20 pm Post subject: |
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Floating point instructions are using st registers similarly to the stack.
fstp is actually an fst and a pop instruction in one package. And fld is the push instruction.
| Quote: | | & do all assembly scripts work on restart, or do some need an AoB scan? Like the CETutorial works evry tym, but in other games, does the address of the disassembly thing change? |
Most games are using static codes, but some games are using JIT. In that case, the code's address will not be static. To make it more confusing, the codes will not be loaded until they are used. Eg the code which is decreasing your health will not be loaded until your health is decreased in the game.
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